The present invention relates to magnetic disk equipment, and more particularly to a magnetic disk apparatus of a constant-density recording type, a magnetic disk used for the apparatus and a servo-writing device for patterning the magnetic disk.
The previously, most common type of recording type for magnetic disk apparatus is based on constant-track-capacity recording. In this type of recording, with the rotation speed of a magnetic disk being constant, the capacity of information per one round or revolution of the of track is the same in both the inner tracks and outer tracks of the disk. In this case, however, the recording density of information is lower with the outer tracks so that the recording efficiency of the magnetic disk is not sufficient.
To solve this problem, the `constant-density` (or `zone-bit`) type of recording method has been proposed in e.g. an article by Mark S. Young entitled "Constant-density Recording Comes Alive With New Chips " in Electronic Design, Nov. 13, 1986, pages 141 to 144. In order to improve the capacity of information of the magnetic disk in particularly a small-sized magnetic disk apparatus, this constant-density recording makes all the tracks including inner tracks and outer tracks have substantially the same density of information. More specifically, in the constant-density recording method, as shown in FIG. 1, the data recording zone z of a data face 1a is divided into plural (e.g. three) zones, and information is recorded so that the recording density in each of the divided zones is substantially constant. The constant-density recording, therefore, provides a greater amount of information per one circle of track in the outer zones of the magnetic disk 1, and thus can increase the recording capacity up to about 1.5 times that of the prior art type of recording method.
FIG. 2 shows the servo face of the magnetic disk used in the prior art dedicated-servo, constant-track-capacity recording type of magnetic disk apparatus. FIG. 3 shows an example of the servo pattern magnetically recorded in an area A in FIG. 2. Additionally, in FIG. 3, the servo pattern is written in solid lines corresponding to a positive magnetic transition and in broken lines corresponding to negative magnetic transition.
In FIG. 3, .alpha. and .beta. are track centers; k's are synchronization information portions provided radially with respect to the center of the disk 1 with no space between the adjacent tracks; and l are servo information portions each of which consists of sets of four servo marks each displaced from the adjacent track by a half track in the radial direction. The synchronization information portions k and the servo information portions l are alternately arranged in the circumferential direction of the disk 1. Several thousands of `servo bytes SB`, each consisting of the adjacent synchronization information portion k and servo information portion l, are arranged on one circle of the servo face 1b.
In the magnetic disk apparatus in which the magnetic disk 1 having the servo face 1b as described above is used, a clock signal is generated by a PLL (Phase Locked Loop) circuit on the basis of the synchronization signal obtained from the synchronization information portion k; this clock signal is used as a reference clock signal or a write clock signal in recording information on the data face 1a and it is also used to generate a window signal (timing signal) for correctly detecting the servo information signal from the servo information portion l. Further, when a servo head 3b passes the servo information portion l, a servo signal is detected using the principle that the signal reproduced from the servo information pattern nearest to the servo head 3b among the four servo information marks has the largest amplitude. In this case, the above clock signal is used as a servo clock signal which is a reference signal for generating the servo signal. Incidentally, the synchronization information portion k being written with no space between the adjacent tracks permits the synchronization information portion to be detected even when the servo head 3b is not located at the track center (e.g. during seeking).